Calcium to phosphorus ratio requirement of 26- to 127-kg pigs fed diets with or without phytase1,2.

ABSTRACT

Two experiments were conducted to determine the effects of calcium to phosphorus (CaP) ratio in diets adequate in standardized total tract digestible (STTD) P on performance of 26- to 127-kg pigs fed diets with or without phytase. Pens of pigs (n = 1,134 in Exp. 1 and n = 1,215 in Exp. 2, initially 26.3 and 25.3 kg) were blocked by body weight (BW) and allotted to treatments in a randomized complete block design. There were 27 pigs per pen with 7 and 9 replicates per treatment in Exp. 1 and Exp. 2, respectively. Treatments were formulated to contain 0.751, 1.001, 1.251, 1.501, 1.751, and 2.001 analyzed CaP ratios in Exp. 1, and 0.751, 1.001, 1.251, 1.501, and 2.001 analyzed CaP ratios in Exp. 2. These correspond to a range of 0.961 to 2.671 and 0.951 to 2.071 STTD CaSTTD P ratios in Exp. 1 and Exp. 2, respectively. Experiment 2 diets contained 1,000 phytase units of Ronozyme HiPhos 2500 (DSM Nutritional Products, Inc., Parsippany, NJ) with release values of 0.132% STTD P, 0.144% total Ca, and 0.096% STTD Ca. Diets contained 122% of NRC (2012) STTD P estimates for the weight range across 4 phases. In Exp. 1, increasing CaP ratio increased (quadratic, P < 0.05) average daily gain (ADG) and average daily feed intake (ADFI). Feed efficiency (GF) worsened (quadratic, P < 0.05) at the highest ratio. Hot carcass weight (HCW) and bone ash increased (quadratic, P < 0.05) while carcass yield decreased (linear, P < 0.10) with increasing CaP ratio. The maximum responses in ADG, HCW, and bone ash were estimated at 1.381, 1.251, and 1.931 analyzed CaP and at 1.821, 1.641, and 2.571 STTD CaSTTD P, respectively. In Exp. 2, increasing CaP ratio increased (quadratic, P < 0.05) ADG and bone ash, and improved GF (linear, P < 0.05). There was a quadratic increase (P < 0.05) in HCW and decrease in carcass yield (P < 0.10). The maximum responses in ADG, HCW, and bone ash were estimated at 1.631, 1.111 to 1.601, and 1.251 analyzed CaP and at 1.751, 1.281 to 1.711, and 1.401 STTD CaSTTD P, respectively. Expressing ADG on a STTD CaSTTD P basis provided a more consistent estimate of the ideal CaP ratio among the 2 studies than analyzed Ca to analyzed P ratio. A STTD CaSTTD P ratio between 1.751 to 1.821 can be used for 26- to 127-kg pigs that are fed diets adequate in STTD P with or without added phytase to maximize growth rate without reducing bone ash.